1. Field of the Invention
The present invention relates to a line status monitoring circuit, a node, a communication system, and a failure occurrence determining method which monitor occurrence of failure in a redundant part of a network.
2. Description of the Related Art
A communication system including a redundant part as shown in FIG. 1 is disclosed in Japanese Patent No. 3730824 and Japanese Patent Laid Open Publication No. 2006-262291.
FIG. 2 shows one example of a communication system including a redundant part as in the above patent documents. A case will be described in which CC (Continuity Check) is performed by Ethernet (R) OAM (Operations Administration Maintenance) in the shown communication system. CC (Continuity Check) refers to processing to send a frame for checking (CC frame) from one end to the other end of a group of switches which is a target of administration and maintenance in order to check connection. CC frames are sent from a node 11 to a node 14 as a multicast frame as well as from the node 14 to the node 11 as a multicast frame. Between a node 12 and a node 13, a plurality of physical lines are vertically bundled and form a Link Aggregation, and a physical connection (line) which is a path of a frame is determined based on an algorithm defined by a frame distribution circuit.
In this communication system, when abnormality occurs in some of lines between the node 12 and the node 13, a connection destination search is performed again in the frame distribution circuit by the Link Aggregation function and a connection destination is changed, so that a CC frame of Ethernet OAM is sent from a sending side to a receiving side through a line having no abnormality.